As this type of hinge mechanism in the prior art, there is a tilt hinge device disclosed in Patent Document 1, for example. The tilt hinge device includes: a mounting member having a base portion and a bearing plate; a rotation shaft at the end thereof having a large diameter portion, a medium diameter portion, and a small diameter portion in this order, and having the medium diameter portion bearing-supported in a bearing hole provided through the bearing plate; a spring washer which is attached to the small diameter portion on the opposite side from the large diameter portion with pinching the bearing plate having the medium diameter portion inserted thereinto; and a pressing washer which is attached to the end of the small diameter portion, and is secured to the small diameter portion and compresses the spring washer, because of the entering of an inner wall-side thickness of the pressing washer into a peripheral groove formed at the outer periphery of the small diameter portion, to thereby clamp the bearing plate and the spring washer against the wall portion of the large diameter portion, wherein the rotation shaft rotates only when a predetermined rotating torque is exerted thereon.